'Usdaw has thousands of members working for Marks & Spencer and the staff now need, more than ever, the representation and support of an independent trade union.
At Newmarket, a spokesman said the company was working with staff to discuss redeploying to other stores, such as Bury St Edmunds, which is 16 miles away, or Cambridge, which is 14 miles from the town.
Stores in Clacton, Essex, and Holloway Road, north London, will close by early next year.
United Kingdom top 10 clothing market shares (%) 2008 and 2018 (by value).
The figure includes 21 that have already closed and 14 stores newly identified for closure.
"Closing stores isn't easy but it is vital for the future of M&S".
M&S has previously described the food arm as exhibiting "ongoing under-performance", with chief executive Steve Rowe saying he will slow expansion of the Simply Food chain as the group battles to restore its high street fortunes.
Last month M&S closed its store on Silver Street in Durham city centre as it switched investment to its branch at the nearby Arnison Centre.
The chain now has 300 clothing and home stores in the United Kingdom and just shy of 600 Simply Food outlets - the majority franchise-owned.
M&S said Bayswater, Fleetwood Outlet and Newton Abbot Outlet will close by the end of July 2018.
The nine stories proposed for closure are set to enter a consultation period with their 626 affected employees.
It was accelerated a year later when Archie Norman, a retail veteran and former boss of Asda, arrived as chairman.
Maureen Hinton, group retail research director at GlobalData, notes after dominating the United Kingdom clothing market for decades, M&S is "perilously close" to losing its status as the number one clothing retailer to Primark.
Making the announcement today, a spokesman said more and more sales were moving online which has contributed to the decision.
Online shopping accounts for 22% of non-food retail sales in the United Kingdom, according to the British Retail Consortium.
M&S has been losing share for more than two decades after achieving its peak clothing market share of 13.5% in the United Kingdom in 1997.
The convenience cuts mean 25 small format food stores will open this year, compared to the 40 previously planned.
Shore Capital analyst Clive Black said the "acceleration of the store closure programme reflects. speeding up of the operating efficiency of the company and the pull forward of some of the cost savings that the company outlined back in November 2017".
Over the past decade M&S has lost 2.2ppt market share as it fights to find a relevant offer for the modern consumer, Hinton continues.